A bathing unit, such as for example a spa or pool, typically includes various components used in the operation of the bathing unit system such as a water holding receptacle, pumps to circulate water in a piping system, a heating module to heat the water, a filter system, an air blower, a lighting system, and a control system for activating and managing the various parameters of the bathing unit components. The circulation system pumps water from the water holding receptacle through the filter system to maintain the body of water at sanitary conditions. In particular, the water passes through the filter system to reduce the accumulation of foreign material, such as hair, soil, or solids, in the pool or spa.
In addition to filtering, bathing unit systems also require regular sanitization in order to maintain hygienic conditions. Allowing sanitation agent levels to either fall below or rise above required levels may result in decreased efficiency of the system. Low levels of chemical sanitizer in the bathing unit can contribute to algae blooms, bacterial breakouts, cloudiness in the water, and chemical imbalances. If left untreated, water-borne bacteria can afflict users of the bathing units with a variety of health problems and illnesses, such as pseudomonas, rashes, hot tub lung, ear infections, etc.
Water sanitation is well known and long practiced. Typical sanitation regimens and processes rely on halogen treatment chemicals to provide disinfecting action. Halogens, and in particular free chlorine and bromine, have recently been the chemicals of choice for treating recreational reservoir water.
Conventional halogen-based systems, to be effective, require that the concentration of halogen (chlorine or bromine for example) be maintained within a specified range, which is typically between 3 ppm (parts per million) and 5 ppm. Maintaining a suitable concentration of halogen in the bathing unit typically requires the user to perform periodic measurements for example by using water testing kits and then taking action to adjust the concentration of the sanitation species so that it lies within the desired specified concentration range. Using these measurements, the user may for example add water to reduce the concentration of halogen and/or may cause an action to take place to increase the concentration of halogen (e.g. by controlling an electrolytic cell to increase the generation of halogen). This is a lengthy process which is not always diligently followed by the user, often resulting in less than ideal water conditions.
To address such deficiencies, various automated devices for measuring the concentration of halogen (chlorine or bromine for example) have been proposed.
U.S. Pat. No. 4,752,740 (“the '740 Patent”) proposes a water chemistry analysis device for pools, spas, and the like which includes an oxidation-reduction potential (ORP) probe and/or a pH (PH) probe disposed in the recirculation/filtration system. The contents of the aforementioned document are incorporated herein by reference. The ORP probe generates an electrical signal directly related to the active form of a sanitizer contained in the water while the PH probe generates and electrical signal that is related to the acidity/basicity level of the water. The signals are used to display information conveying measured ORP levels against upper and lower limits corresponding to “more than necessary” and “less than necessary” levels of sanitizer in the water and to convey measured PH levels against upper and lower limits corresponding to “lower acidity than optimum” and “higher acidity than optimum” levels of water.
A deficiency associated with devices of the type described in the '740 Patent is that the ORP probe and the PH probe are physical probes that are in contact with the water of the bathing unit. These physical probes are prone to mechanical wear and tear and deposits on the physical probes, which naturally occur in bathing unit environment, often affect the precision of the measurements taken and require frequent calibration.
Another approach that has been proposed more recently, and which may reduce or eliminate the need for physical probes in the water of the receptacle, is to make use of UV spectrometry to measure the concentration of halogen in spas. Generally, the approach includes emitting a light at a specific wavelength through a sample of water and measuring the level of absorption as the light travels through the sample of water. Most chemical compounds absorb light in a manner that varies according to the wavelengths of the light used and the amount of the chemical compound present. The measured level of absorption is used in combination with the spectral signature of the halogen sought to be measured to derive a concentration of the halogen in that sample of water. While in theory such approach may appear simple, in practical bathing unit applications the concentrations of halogen being measured are low and the difference between a suitable concentration of halogen and one that is unsuitable is small. As a result, variations in extraneous factors unrelated to the concentration of the halogen in the water may in some cases materially influence the precision of the measurements obtained rendering them unsuitable for distinguishing between a suitable concentration of halogen and one that is unsuitable.
U.S. Pat. No. 8,212,222 (“the '222 Patent”) proposes a method of measuring chlorine concentration in a solution that aims to compensate for a specific one of these extraneous factors, namely the effect of temperature on the precision of the measurements. The contents of the aforementioned document are incorporated herein by reference. More specifically, the '222 Patent proposes a method of measuring chlorine concentration in a solution by making first and second measurements of transmission of ultraviolet light at a selected wavelength through respective first and second samples of the solution held in a “cuvette”, where the first and second solution samples are heated to different temperatures. More specifically, the approach proposed by the '222 Patent exploits the variability in the equilibrium point of HOCl/OCl— with temperature and is premised on the absorption spectra of strongly ionised salts, such as nitrates and carbonates dissolved in solution, not changing with temperature. By taking the difference (absolute difference or ratio) from a single wavelength, for example, at 293 nanometers (nm) (the absorption peak of the OCl— species) at two different temperatures, a measurement of the level of OCl— that is less sensitive to water temperature can be derived.
A deficiency with methods and devices of the type described in the '222 Patent is that they require a complex arrangement including a valve arrangement to place sequential samples of the solution in a “cuvette”, a heat exchanger to heat one of the samples and not the other, and components for sequentially taking measurements of the samples to obtain two absorption measurements. The complexity of the arrangement proposed in the '222 Patent including the requirement to provide a valve system and a heat exchanger, adds cost to the device. Moreover, the valve arrangement, which includes mechanically moving parts, is prone to mechanical wear and tear, which may reduce the useful life of the arrangement.
Another deficiency with methods and devices of the type described in the '222 Patent is that while the solution proposed may potentially compensate for water temperature effects, the precision of the measurements remains sensitive to other extraneous factors unrelated to the concentration of the halogen. While controlled environments (such as laboratories) may make it possible to achieve suitable levels of precision even at low levels of halogen concentration by eliminating variations of certain extraneous factors, achieving such level of control is not suitable for practical bathing unit environments.
Against the background described above, there is a need in the industry to provide a method, device and system for monitoring halogen levels in bathing units that alleviate at least in part the problems associated with existing methods, devices and systems.